Internal shoe drum brake



May l, 1945.

INTERNAL SHOE DRUM BRAKE Filed oct'. 1a, 194s' nf, g

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2 Sheets-Sheet l AMay 1, 41945. 4 1 c. cHQulNGs y 2,374,651

INTERNAL SHOE DRUM BRAKE Filed Oct. 18, 1945 2 Sheets-Sheet 2 /N VE NTUI? y 5.52/5 6'. (//Qa/A/GS Patented May 11,1945

o f lN'rEnNAL suon DRUM BRAKE Leslie Cyril Chouings, Leamington Spa,England, aosignor to Automotive Products ConmanyV Limited.

Application october 1s, 194s, serial Noisosnas j In Gres: Britainoctober 9, 1942 s claims. (ci. issrsi This invention relates to internalshoe drum brakes of the kind comprising two arcuate shoes each having ananchorage abutment atone end, both shoes extending from their abutmentsin the same circumferential ing operated by a single spreading meansacting directly on to the free end of one shoe, and through a linkage onto the free end of the sec. ond shoe.

It is the object of the invention to provide a' simple and elcient brakeof this kind In a brake which is of the kind referred to and in whichthe linkage comprises two interconnected bell-crank levers, -the firstof which levers is acted upon by the spreading means, while the secondthe second shoe with one of its ch'aracterised by and engages a iixedabutment arms, the present invention is the fact that the firstbell-crank lever is pivotally mounted on the-xed support of the brake,and, through its interconnection with the other bell-crank lever, limitsthe yinward movement of the second shoe when the brake is released. Y

Preferably the fixed abutment comprises an adjustable stop serving toadjust the drum clearance of the second shoe, said adjustable stopconveniently comprising a strut of variable length operatively connectedbetween the second bell-crank lever and the anchorage abutment of therst shoe. 'I'he spreading means may act as an anchorage for the firstbell-crank lever when the brake is released. Moreover at least one armof each bell-crank lever is preferably double so as to extend on bothsides of a radial web forming part of the second shoe, said bell-cranklevers conveniently being connected together by a thrust membercomprising a pair of strips held in spaced parallel relationship so asto extend alongside opposite side surfaces of the shoe web. Movement ofthe shoe in an axial direction is preferably prevented by a springiinger, which resiliently tact with a shoe-locating projectoncarried bythe iixed support of the brake, the shoe-locating projection beingprovided with a screw-threaded adjustment member against which the shoeweb bears slidably. If desired a single adjusting means may serve tomove the anchorage of the iirst shoe and the adjustable stop for thesecond bell-crank lever.

'I'he invention is illustrated in the accompanying drawings, in which:

Figure 1 is an elevation of one construction of brake, the drum beingshown in section;

sense and the shoes besectional plan taken ied adjusting device for thelower ends of the is pivoted on the free end of shoes; and l Figure 4 isa fragmentary sectional plan taken on the line l-I of Figure 3.

A drum Il of the usual cylindrical form constitutes the rotating elementof the brake, as shown in Figure 1, and is arranged to be engaged by apair of rigid arcuate brake shoes, the'ilrst of which is indicated at II.and the second at I2. Each shoe is of the usual T shape incross-section comprising a web' I3 and a curved flange I 4, to whichlatter the lining I5 of the brake -shoe is attached. The usual xedsupport of the brake, i. e. that part which does not rotate and 2s pinI9,

maintains said web in con-A serves as a mounting for the brake shoes,comprises a substantially tubular member I6 arranged to be secured tothe axle casing or other convenient xed part of the vehicle, saidtubular member I6 being formed integrally with a depending bracket I'land an upwardly extending bracket I8. A circumferentiall'y groovedanchor fixedly mounted upon the bracket Il, is arranged to be engaged bya notch 20 in the end of the web I3 of the shoe said shoe to moveangularly into and out of engagement with the interior of the drum I 0.A similar fixed anchor 2I is provided for engagement by the notchedportion 22 of the shoe I2. Spreading meansindicated generally at 23, aresecured to the lbracket I8 and conveniently com. prise a hydrauliccylinder 24 containing a pair of pistons 25 and 26 adapted to be spreadapart by admitting liquid under pressure through an inlet opening 21.The piston 25 is formed with a shoulder 28 arranged to abut against thecorresponding end of the cylinder -24 so as to enable said piston to actas an anchorage; in the case of the piston 26 a knurled head 29 providesa shoulder 30 adapted to engage the end of the cylinder for a similarreason, but the head 29 is in addition arranged to serve as anadjustment for the first l'shoe II. Thus a stem member 3|,screw-threaded into the piston 26, is slotted diametrally at 32 toembrace the end of the web I3 of the shoe Il, so that by rotating thehead 29 the stem member 3I can be forced outwards to the desired extentin order to adjust the clearance between the lining I5 and thedrum I0. Aspringnger 33 preserves the adjustment of the .head 29 in the usualmanner.

The means used for applying the second shoe I2 comprise a rst bell-cranklever 34 mounted I I, thereby allowing.

' the fixed support. The bell-crank lever 34 comprises an upwardlydirected arm 36 engaging with the piston 25, and also a substantiallyhorizontal arm 31 which is double or bifurcated so as to extend on bothsides of the web of the shoe I2, said arm 31 beingv formed at its outerend with a notch 38 adapted to engage pivotally with the narrow butrounded upper end of a thrust member 39. This is also of doubleconstruction so as' to engage with both parts of the arm 31, andcomprises a pair of strips 49 held in parallel relationship by spacingmembers 4l. The lower end of the thrust member 39 engages with a secondbell-crank lever 42. The second bell-crank lever 42 comprises a pairofvidentical substantially triangular plates 43 disposed one on eachside of the web I3 of the shoe I2 and pivoted to the latter by means ofa fulcrum pin 44. The lower end of the thrust member 39 pivotallyengages with notches 45 in what constitutes the substantially horizontalarm 46 of the bell-crank lever, while a substantially vertical arm,indicated at 41, is formed with a notch 48 which engages pivotally withthe end of the bifurcated portion 49 of a fixed abutment deviceindicated generally at 59.

The fixedabutment device 59, which operates in conjunction with theanchorage I9, is arranged to be adjustable and comprises a nonrotatablebearer member having an arcuate head portion 52 arranged to engage thegroove in the anchor pin I9 and a cylindrical spigot 53; mountedrotatably upon the spigot 53 so as to bear against a shoulder 54 is anadjusting sleeve 55 having a knurled head portion 56 engaged by aretaining spring nger `51. The adjusting sleeve 55 is internallyscrew-threaded for engagement with a corresponding thread upon theoutside of a stem 58, which latter extends through a slotted retaininglug 59 and is formed with the bifurcated portion 49 to-embrace the endof the web of the shoe I2. Thus the bifurcated portion 49 serves as afixed but adjustable anchorage for the arm 41 of the bell-crank lever42, and, owing to the provision of the slotted lug 59, it also acts toprevent lateral displacement of the lower end of the shoe I2 in adirection parallel with the drum axis.

Lateral displacement of each of the shoes II and I2 is also prevented bya shoe-locating projection 69 secured to the ilxed support I6 by screws6I. The extremity of the projection 69 is threaded to receive a grubscrew 62, against the inner end 63 of which the web I3 of the brake shoeis adapted to bear, as will be seen more clearly in Figure 2. Thev shoeis held resiliently in this position by a spring finger 64 having areinforced end portion 65, said nger being secured to the projection 69by a a pair of screws, one of which is indicated at 66. A lock nut 61preserves the adjustment of the grub screw 62.

The usual two pull-olf springs which draw the shoes together forreleasing the brake are indicated at 68 and 69. Each is anchored at oneend to a pin 19 projecting from the web of the shoe I2,` and at itsother end said spring engages with a dead-centre link in the form of asubstantially triangular plate 1I. This plate is pivoted at 12 to theweb I3 of the shoe II. The turned-over end of the spring engages with anotch 13 in the plate, so that by rotating said plate the axis of thespring can be caused to pass the axis of the pin 12. The springnaturally tends to move the plate 1I in either direction away from thisdead-centre position, but such movement in one direction is prevented bythe engagement of the corner portion 14 of the plate with the inside ofthe flange I4, thus retaining the spring in its operative stretchedcondition. To release the tension in the spring the corner portion 14 ismoved away from the ilange I4, and after the dead-centre position hasbeen passed the tension in the spring can be completely released beforethe spring is disconnected.

The normal forward direction of drum rotation of the brake shown inFigure l is clockwise, and when the spreading means 23 are operated withthe drum rotating in this direction the first shoe II acts as a simpleleading shoe taking its abutment upon the anchor pin I9. At the sametime outward movement ofthe piston 25 causes the first bell-crank lever34 to be moved in an anti-clockwise direction, thus moving the thrustmember 39 in a downward direction. `The bifurcated portion 49 of thefixed abutment device 59 then acts as an anchorage, so that the secondbell-crank lever 42 is caused to move in an f' anti-clockwise .directionabout said bifurcated portion, thus forcing the pin 44 towards the leftand applying the second shoe I2 to the drum I9; during this action theupper end of the shoe I2 engages the anchor pin 2 I, so that this shoealso acts in a leading sense for forward rotation of the drum. With thedrum I9 rotating in an anti-clockwise direction both shoes II and I2operate as trailing shoes, the shoe I2 being moved outwards intoengagement with the drum I9 by the action of the bellcrank levers 34 and42. As mentioned above, the first shoe II is adjusted by means of thehead 29, and it will now be appreciated that the clearance of the shoeI2 is regulated by turning the head 56 so as to vary the operativelength of the xed abutment device 59, the bell-crank lever 34 taking itsabutment upon the cylinder 24 through the medium of the external part ofthe hydraulic piston 25.

If desired the xed abutment device 59 may be arranged to eiTectsimultaneously the adjustment of both shoes II and I 2, and a modiedform of shoe anchorage embodying this feature is shown in Figures 3 and4. A somewhat V-shaped housing 15 is secured to the bracket I1 by a pairof studs and nuts 16, and is formed with a pair of mutually inclinedbores 11 and .19 each containing .a corresponding freely slidableplunger member 19 or 89. The plunger member 19 has a head 8I, which isslotted at 82 to embrace the web of the first shoe II, the base of theslot being convex to engage pivotally with a semi-circular notch 83formed in the lower end of the shoe Il. The outer end of the plungermember is slotted diametrically, as indicated at 84, so as to receivethe web at the lower end of the second shoe I2, the pair of end surfaces85 being arranged to bear each against a convex surface 86 at the lowerpart of the corresponding plate 413 constituting the bell-crank lever42. The adjacent end part of the housing 15 is also slotted atdiametrically opposite positions to accommodate the web of the shoe I2,thus locating said shoe against axial displacement. The inner ends ofthe plungers 19 and 89 are sloped, as indicated at 81, forengagementjwith a cam member 88 having a pair of ears 89 and 99, thesebeing of triangular shape and being arranged to slide withincorresponding grooves 9| and 92 formed in the housing 15. The cam member8B is screw-threaded at its central part and constitutes a nut mountedupon a screw-threaded stem 93 having a head 94 adapted to bear againstan annular surface 95 of the housing 15; axial displacement of thestem93 in an outward direction is prevented by a plate 96. When the brake isin operation the plunger member 'I9 constitutesl the anchorage abutmentfor the shoe Il, while the plunger member 80 forms a correspondinganchorage for the bell-crank lever I2.

When it is desired to readjust the shoes in order to take up wear of thelinings the stem 93 is rotated by means of a suitable key applied to itssquared end portion 91, the direction of rotation being such that theears 89 and 90 of the cam member 88 force apart the plunger members 19and 80 to the requisite amount. y

It will be understood that the arrangements which have been describedare given merely by way of example and that the constructionmay bemodified to suit requirements. For instance, various forms of spreadingmeans may be employed, such, for example, asthe mechanical expanderdevice described in United States of America patent specication No.2,238,361, dated April 15,

The improved brake is more particularly applicable to the steeringmechanism of endless. track vehiclesin which brakes are used to retardthe movement of the track on one or other side or the vehicle forsteering purposes. Itsuse is not, of course, limited to this particularapplication.

What I claim is:

1. In a Ibrake including a support, a shoe mounted on the support, anactuator, and a fixed abutment device on the support at the opposite endof the shoe from the actuator, means for exerting force against the endof the shoe remote from the actuator comprising two interconnectedbell-crank levers, the rst of which is acted upon by the actuator and ispivotally mounted on the support, the second of which is pivoted on theremote end of the shoe and engages the iixed abutment device with one ofits arms, the first bell-crank lever being adapted through itsinterconnection With the other bell-crank lever to limit the inwardmovement of the shoe when the brake is released, said abutment deviceincluding an adjustable stop engaging the second bell-crank lever andwhich serves to adjust the clearance of the shoe.

2. A brake as claimed in claim 1, wherein the 'mounted on the support,an actuator, and an anchor on thesupport' opposite the actuator, incombination, means'for' exerting force against the end of one shoe nearthe anchor comprising two interconnected bell-crank levers, the rst ofwhich is acted upon by the actuator and is pivotally mounted on thesupport, and the4 second of which is pivoted on the remote end of theshoe and engages the anchor with .one of its arms, the rst bell-cranklever being adapted through its interconnectionwith the second bellcranklever to limit the movement of the shoe when the brake is released, anda single adjusting means serving to move the anchorage ofA crank levers,the first of which is acted upon by movement of the shoe when the brakeis reactuator acts as an anchorage for the lrst belly crank lever whenthe brake is released.

3.x In a brake including a support, two shoes the actuator and ispivotally mounted on the support, the second of which is pivoted on theremote end of the shoe and engages the xed abutment with one of itsarms, the iirst bell-crank lever being adapted through itsinterconnection with the other bell-crank lever to limit the inwardmovement of the shoe when the brake is released, and means forpreventing movement of the shoe in an axial direction comprising aspring finger which resiliently maintains the shoe web in contact withthe support.

5. In a brake including a support, a shoe mounted on the support, anactuator, and a iixed abutment on the support at the opposite end of theshoe from the actuator, means for exert-V ing force against the end ofthe shoe remote from the actuator comprising two interconnected:bellcrank levers, the yfirst of which is acted upon by the actuator andis pivotally mounted on the support, the second of which is pivoted onthe remote end of the shoe and engages the fixed abutment with one ofits arms, the iirst bell-crank lever being adapted through itsinterconnection with the other bell-crank lever to limit the inwardleased, and means for preventing movement of the shoe in an axialdirection comprising a projection on said support having thereon a.screw threaded adjustment member against which the shoe web lbearsslidably, and a spring nger which resiliently maintains the shoe web incontact with said adjustment member.

LESLIE CYRIL CHOUINGS.`

